In May 2001, the Federal Aviation Administration released a comprehensive Special Federal Aviation Regulation (SFAR No. 88) requiring all airframe manufacturers and Supplemental Type Certificate (STC) holders to conduct a safety review of fuel system components. Included in the regulation were requirements to prepare special maintenance inspections that operators of transport aircraft would use to determine the continued safety and airworthiness of the fuel system on their respective aircraft. Since the release of SFAR No. 88 in May of 2001, aviation fuel system manufacturers have embarked on a comprehensive effort to address the fuel system safety requirements specified in the regulation.
Among other requirements, SFAR No. 88 states that no ignition source may be present in an aircraft fuel tank system where catastrophic failure could occur due to ignition of fuel or vapors. In pre-SFAR No. 88 fuel tank designs, electrical wires were routed through a fuel system in hard-plumbed metal conduits that separated the wires from the aviation fuel. Among other limitations, hard-plumbed metal conduits are relatively inflexible, which increases the complexity of the routing and the difficulty of manufacture. Another limitation of metal conduits is their inability to isolate electrical wires when the sleeving and insulation on the wires is worn or damaged. Worn electrical wires may arc through the conductive metal components of the conduits and into the fuel tank ullages creating a risk of fire. Since current metal conduits fail to satisfy the safety requirements of SFAR No. 88, a need exists for a relatively flexible conduit assembly that electrically isolates a worn or damaged electrical wire within the conduit from the flammable contents of a fuel tank.